The present invention relates to a fluidized bed technique for use in cooling high temperature waste gases from industrial processes. Heat recovery may be effected from the hot waste gases, which are of a temperature in excess of about 800.degree. C.
It has previously been proposed to use fluidized bed technology for heat recovery from hot waste gases of various industrial processes. Problems are associated with the use of fluidized bed cooling of waste gases, such as, for example; (1) the fluidized bed gas distributor is prone to deposition and plugging and mechanical failure due to contact with the waste gases and contaminants therein, and such distributors are expensive, complex fabrication items, (2) heat transfer tubes (heat transfer surfaces) in such fluidized beds are also prone to corrosion, erosion, and fouling in hot, dirty, fluidized bed environments, (3) inefficient heat recovery is achieved due to the need for gas precooling by dilution in some systems and well-mixed, single-stage heat transport behavior, and (4) the particular material used in fluidized bed may agglomerate due to deposition, resulting in potential bed defluidization or clinker formation.
It is an object of the present invention to provide a method and apparatus using fluidized bed techniques that solve the aforementioned four major problems and provide an efficient means for cooling of hot waste gases. In the present invention, the gas distributor is not contacted by the hot waste gas, with a fluidized bed being heated mainly by radiation from above, and relatively small amounts of cooler gas used to fluidize a bed of solid particulate material. Plugging, deposition and mechanical design considerations are based on conventional practice, depending on the extent of fluidizing air preheat or the ratio of air dilution of waste gas in the fluidizing gas stream. Where heat transfer tubes are present in the fluidized bed, in the present invention, such tubes are not subjected directly to the hot waste gases, minimizing corrosion and fouling concerns, while tube erosion is limited by operating with a relatively gentle fluidizing condition in the bed. Also, heat transfer, in the preferred embodiment of the present invention is promoted by a countercurrent heat transfer, especially as a high temperature radiant cooler stage. The present fluidized bed technique can be coupled with conventional staged fluidized bed heat exchanges for high overall heat recovery effectiveness, depending upon the deposition nature of the waste gas. Additionally, bed material agglomeration is avoided by limiting direct contact made between the solid particulate material of the fluidized bed and the hot waste gas.